5o8 ANGIOSPERMAEMONOCOTYLEDONES 



anthers empty their pollen-grains under water ; these are cylindrical in shape and 

 bent like a knee ; they possess no extine, and their specific gravity is so small that 

 they rise at once to the surface of the water. 



In the second (female) stage of the spadix its stalk has elongated so greatly that 

 the now mature ovary reaches the surface of the water, where the pollen is blown to 

 it by the wind. Much as in Vallisneria the stalk of the spadix draws back below the 

 surface of the water when pollination has been effected, and the fruits mature there. 



2957. R. rostellata Koch. (Delpino u. Ascherson, op. cit. ; H. Schenck, 

 op. cit.) The construction of the flowers and the course of maturation of the stigmas 

 and anthers are the same as in the preceding species, but this one is also described 

 as homogamous or protogynous. The stalk of the spadix remains short and straight 

 and does not curl up spirally. Pollination is no doubt again effected by floating 

 pollen, but no direct observations have been made. 



967. Zannichellia Mich. 

 Flowers monoecious and hydrophilous. The pollen-grains possess no extine. 



2958. Z. palustris L. (Kerner, 'Nat. Hist. PI.,' Eng. Ed. i, II, pp. 130-2; 

 Roze, J. Bot., Paris, i, 1887, pp. 296-9.) Tritzschke states that the pollen-grains 

 possess no extine, hence it is highly probable that the species is hydrophilous. The 

 male flower consists of one exposed stamen, the female of a cup-shaped involucre 

 with four carpels, possessing short styles, and stigmas uniting to form a crooked 

 funnel. As long as the pollen-grains remain in the closed anthers they are spheroidal 

 in shape, but as soon as they leave those receptacles they become tubes which force 

 their way to the stigmas. Each of the latter is a triangular, rather large lobe ; Roze 

 says that three or four such lobes meet, forming a funnel to catch the floating pollen. 



968. Zostera L. 



Flowers monoecious and hydrophilous. The pollen-grains possess no extine. 



2959. Z. marina L. (Clavaud, ' F^cond. du Zostera '; A. Engler, Bot. Ztg., 

 Leipzig, xxxvii, 1879, pp. 654-5; H. Schenck, op. cit., p. 127; Delpino, 'Ult. oss.,' 

 II.) The numerous unisexual flowers of this species possess no perianth; they 

 are sessile on a membranous foliar axis, and surrounded by an involucre, which is 

 produced into a linear expansion. The flowers are arranged on the axis as single 

 anthers and ovaries in two longitudinal rows, the male flowers alternating with the 

 female ones above and at the side. This position also makes it possible that each 

 two adjacent anthers and ovaries together form a hermaphrodite flower. The 

 inflorescences are protogynous. In the first stage, the two filiform furcate stigmas 

 project 3 mm. from the involucre, while the anthers are still closed. The anthers 

 then suddenly dehisce and shed all their pollen-grains simultaneously. These possess 

 no extine, and form thread-shaped clumps which float about on the surface of the 

 water, and are caught by the stigmas of plants still in the first (female) stage. The 

 stigmatic branches are made up of wedge-shaped, outwardly curved cells, which 

 become soft at the spot where a pollen-grain adheres and render it possible for the 

 pollen-tube, hitherto a short, blunt process, to penetrate. When pollination has been 

 effected the styles fall off. 



II 



